The Federal Reserve kept interest rates pinned near zero on Wednesday and made a bold, new promise: to keep them there until inflation is on track to "moderately exceed" the U.S. central bank's 2 percent inflation target "for some time."

The new guidance marks a monetary policy shift, first announced by the Fed last month, that is aimed to offset years of weak inflation and allow the economy to keep adding jobs for as long as possible.

"Effectively what we are saying is that rates will remain highly accommodative until the economy is far along in its recovery," Fed Chair Jerome Powell said in a news conference following the release of the central bank's latest policy statement and economic projections.